Systems with pairs of voltage level shifter switches to couple voltage level shifters to anti-aliasing filters

ABSTRACT

A battery-operated device comprises: a first battery cell having a voltage; a second battery cell having a voltage; a first anti-aliasing filter operable to be coupled to the first battery cell; a second anti-aliasing filter operable to be coupled to the second battery cell; an analog-to-digital converter operable to be coupled to the first anti-aliasing filter during a first period of time or the second anti-aliasing filter during a second period of time different than the first period of time; and wherein the second anti-aliasing filter is charged during the first period of time and the first anti-aliasing filter is charged during the second period of time.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. application Ser. No.16/173,883, filed Oct. 29, 2018, which is hereby incorporated byreference in its entirety.

BACKGROUND

In many battery powered applications such as, for example, electricvehicles employing power systems comprising multiple battery cells,circuits are employed to monitor the battery cells, and to read thevoltages of the battery cells. The voltages of the battery cells aredigitized to provide digital data indicative of the voltages of thebattery cells.

SUMMARY

In accordance with at least one example embodiment, a battery-operateddevice comprises: a first battery cell having a voltage; a secondbattery cell having a voltage; a first anti-aliasing filter operable tobe coupled to the first battery cell; a second anti-aliasing filteroperable to be coupled to the second battery cell; an analog-to-digitalconverter operable to be coupled to the first anti-aliasing filterduring a first period of time or the second anti-aliasing filter duringa second period of time different than the first period of time; andwherein the second anti-aliasing filter is charged during the firstperiod of time and the first anti-aliasing filter is charged during thesecond period of time. In another example embodiment, theanalog-to-digital converter outputs a digital representation of thevoltage of the first battery cell at the first period of time. In anexample embodiment, the analog-to-digital converter outputs a digitalrepresentation of the voltage of the second battery cell at the secondperiod of time. In another example embodiment, the battery-operateddevice is an electric vehicle.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of various examples, reference will now bemade to the accompanying drawings in which:

FIG. 1 shows circuitry for monitoring the voltage of multiple batterycells, in accordance with various examples;

FIG. 2 shows circuitry usable to monitor the voltage of multiple batterycells, in accordance with various examples;

FIG. 3 shows circuitry for monitoring the voltage of multiple batterycells, in accordance with various examples; and

FIG. 4 shows a system for monitoring the voltage of multiple batterycells, in accordance with various examples.

DETAILED DESCRIPTION

Some conventional circuits for monitoring multiple battery cells andconverting their respective voltages into digital data makes use ofmultiple anti-aliasing filters, with one anti-aliasing filter for eachbattery cell being monitored. Such circuits have relatively low latencybecause there is sufficient time for the anti-aliasing filters to chargeand for transients to die out before a value is read and digitized foreach battery cell. However, such circuits utilize a relatively largearea because of the multiple anti-aliasing filters. To reduce circuitdie area, some circuits for monitoring battery cells employ for eachgroup of battery cells (e.g., a group may consist of four battery cells)a single anti-aliasing filter, but the resulting circuit configurationmakes use of multiplexing in which the latency is reduced because of thesettling time needed for the single anti-aliasing filter. Examplesdescribed herein utilize two anti-aliasing filters for a group of fourbattery cells such that when one anti-aliasing filter is being charged,the other is providing its output to an analog-to-digital converter. Inthis way, examples achieve a relatively low latency and efficient use ofdie area.

FIG. 1 depicts a system 100 to monitor the voltage of multiple batterycells. The system 100 may find use in a variety of applications,including electric vehicle (EV) applications, and more particularly intandem with battery cells used in EVs. In the example of system 100,four battery cells are shown: a first battery cell 102, a second batterycell 104, a third battery cell 106, and a fourth battery cell 108. Inmany applications such as, for example, in automotive applications, abattery powered system includes more than four battery cells. Theexamples described herein are applicable to battery powered systemshaving more than four battery cells.

Four channels, labeled CH1, CH2, CH3, and CH4 in FIG. 1, each providedigital information indicative of the voltage of their respectivebattery cells. The channels CH1, CH2, CH3, and CH4 provide,respectively, digital information indicative of the voltage of the firstbattery cell 102, the second battery cell 104, the third battery cell106, and the fourth battery cell 108. An analog-to-digital converter 110and circuit modules, to be described below, provide filtering andsampling functions for generating the digital information on thechannels CH1, CH2, CH3, and CH4 indicative of the voltages on thebattery cells 102, 104, 106, and 108.

A first voltage level shifter 112 comprises a differential output port,labeled 114 and 116, and a differential input port, labeled 146 and 148.A first anti-aliasing filter 118 comprises a differential input port,labeled 120 and 122, and a differential output port, labeled 124 and126. A first pair of voltage level shifter switches 128 couples thedifferential output port 124 and 126 of the first voltage level shifter112 to the differential input port 120 and 122 of the firstanti-aliasing filter 118. A unity gain differential buffer 130 comprisesa differential input port, labeled 132 and 134, and a differentialoutput port, labeled 136 and 138. A first pair of anti-aliasing filterswitches 140 couples the differential output port 124 and 126 of thefirst anti-aliasing filter 118 to the differential input port 132 and134 of the unity gain differential buffer 130. The analog-to-digitalconverter 110 is coupled to the differential output port 136 and 138 ofthe unity gain differential buffer 130.

In the example of FIG. 1, the analog-to-digital converter 110 comprisesa sigma-delta modulator 142 coupled to the differential output port 136and 138 of the unity gain differential buffer 130, and a cascadedintegrator comb filter 144 coupled to the sigma-delta modulator 142.Other examples can utilize different types of analog-to-digitalconversion.

The system 100 further comprises a first bulk current injection filter150 comprising a differential output port, labeled 152 and 154, coupledto the differential input port 146 and 148 of the first voltage levelshifter 112. The first bulk current injection filter 150 furthercomprises a differential input port, labeled 156 and 158. The firstbattery cell 102 is coupled to the differential input port 156 and 158of the first bulk current injection filter 150. A first pair of batteryswitches 160 couples the first battery cell 102 to the first currentinjection filter 150. In the example of FIG. 1, the first battery cell102 is further coupled to the first current injection filter 150 by wayof a first common-mode noise filter 162.

The system 100 further comprises: a second voltage level shifter 164comprising a differential output port, labeled 166 and 168; a secondanti-aliasing filter 170 comprising a differential input port, labeled172 and 174, and a differential output port, labeled 176 and 178; asecond pair of voltage level shifter switches 180 to couple thedifferential output port 166 and 168 of the second voltage level shifter164 to the differential input port 172 and 174 of the secondanti-aliasing filter 170; and a second pair of anti-aliasing filterswitches 182 to couple the differential output port 176 and 178 of thesecond anti-aliasing filter 170 to the differential input port 132 and134 of the unity gain differential buffer 130.

The system 100 further comprises: a third voltage level shifter 184comprising a differential output port, labeled 186 and 188; a third pairof voltage level shifter switches 190 to couple the differential outputport 186 and 188 of the third voltage level shifter 184 to thedifferential input port 120 and 122 of the first anti-aliasing filter118; a fourth voltage level shifter 192 comprising a differential outputport, labeled 194 and 196; and a fourth pair of voltage level shifterswitches 198 to couple the differential output port 194 and 196 of thefourth voltage level shifter 192 to the differential input port 172 and174 of the second anti-aliasing filter 170.

The system 100 further comprises: a second pair of battery switches 200to couple the second battery cell 104 to the second voltage levelshifter 164, the second battery cell 104 coupled to the second voltagelevel shifter 164 by way of a common-mode noise filter 202 and a bulkcurrent injection filter 204; a third pair of battery switches 206 tocouple the third battery cell 106 to the third voltage level shifter184, the third battery cell 106 coupled to the third voltage levelshifter 184 by way of a common-mode noise filter 208 and a bulk currentinjection filter 210; and a fourth pair of battery switches 209 tocouple the fourth battery cell 108 to the fourth voltage level shifter192, the fourth battery cell 108 coupled to the fourth voltage levelshifter 192 by way of a common-mode noise filter 211 and a bulk currentinjection filter 212.

The system 100 further comprises a demultiplexer 214. The demultiplexer214, depending upon its state, provides the output of theanalog-to-digital converter 110 to one of the channels CH1, CH2, CH3, orCH 4. Additional filtering can be performed on the data provided on thechannels CH1, CH2, CH3, or CH 4, for example by digital filters 218,220, 222, and 224.

The system 100 further comprises a controller 216. The controller 216 isa finite state machine, where its functionality can be realized byhardware only, by hardware and firmware, by hardware and software, or acombination thereof. When the battery cells are to be monitored, thecontroller 216 closes the pairs of battery switches (160, 200, 206, 209)to connect the battery cells to the various circuit modules. Thecontroller 216 sequences the states of the voltage level shifterswitches (128, 180, 190, 198), the anti-aliasing filter switches (140,182), and the demultiplexer 214 so that data on each channel correspondsto its corresponding battery cell, where CH1 monitors the first batterycell 102, CH2 monitors the second battery cell 104, and so forth.

The controller 216 controls the states of the voltage level shifterswitches (128, 180, 190, 198) and the anti-aliasing filter switches(140, 182) so that when one of the anti-aliasing filters is being readby the analog-to-digital converter 110, the other anti-aliasing filteris being charged. This reduces latency in monitoring the battery cellswhile utilizing only two anti-aliasing filters to reduce die area. Aswill be described in more detail below, the controller 216 is configuredto: switch on and off the first and second pairs of voltage levelshifter switches (e.g., 128 and 180); and switch on and off the firstand second pairs of anti-aliasing filter switches (e.g., 140 and 182).

More particularly, the controller 216 is configured to switch on and offvarious combinations of the voltage level shifter switches, as follows.The controller 216 switches on and off the first and third pairs ofvoltage level shifter switches (128 and 190) in complementary fashion.By complementary fashion, it is meant that the first pair of voltagelevel shifter switches 128 is switched on when the third pair of voltagelevel shifter switches 190 is switched off, and the third pair ofvoltage level shifter switches 190 is switched on when the first pair ofvoltage level shifter switches 128 is switched off. The controller 216further switches on and off the second and fourth pairs of voltage levelshifter switches (180 and 198) in complementary fashion. Furthermore,the controller 216 switches on and off the first and second pairs ofanti-aliasing filter switches (118 and 170) in complementary fashion.This complementary switching of the first and second pairs ofanti-aliasing filter switches (118 and 170) results in charging thesecond anti-aliasing filter 170 when the first anti-aliasing filter 118is coupled to the differential input port 132 and 134 of the unity gaindifferential buffer 130, and charging the first anti-aliasing filter 118when the second anti-aliasing filter 170 is coupled to the differentialinput port 132 and 134 of the unity gain differential buffer 130.

The above way in which the controller 216 controls the various switchescan be described in more detail by the following example, where thecontroller 216 includes a two-bit counter to sequentially sequencethrough the two-bit counter's four states, and where the controller 216evaluates a set of Boolean functions in response to each of the fourstates in order to set the states of the various switches and thedemultiplexer 214. Based upon the evaluation of the set of Booleanfunctions in response to the two-bit counter, the controller 216sequences the states of the voltage level shifter switches (128, 180,190, 198), the anti-aliasing filter switches (140, 182), and thedemultiplexer 214. The sequencing of states and the set of Booleanfunctions are described as follows.

Let the ordered Boolean pair (S₁,S₀) represent the four states of thetwo-bit counter, with S₁ and S₀ given by: (0,0), (0,1), (1,0), and(1,1). The controller 216 generates a gray code based upon the Booleanpair (S₁,S₀), where the controller 216 uses the gray code to generateinputs to the set of Boolean functions. The controller 216 generates thegray code based on the two-bit counter by the following mapping (S₁,S₀)(G₁,G₀): (0,0)→(0,0), (0,1)→(0,1), (1,0)→(1,1), and (1,1)→(1,0).

The set of Boolean functions can be described as follows, where “-”denotes a Boolean complement, a product denotes a logical AND, a sumdenotes a logical OR, and where a Boolean function evaluated to aBoolean “1” denotes that its corresponding switch is on and whenevaluated to a Boolean “0” denotes that its corresponding switch is off:

G₁G₀+(−G₁)(−G₀) for the state of the first anti-aliasing filter switch140;

(−G₁)G₀+(G₁)(−G₀) for the state of the second anti-aliasing filterswitch 182;

−G₀ for the state of the first pair of voltage level shifter switches128;

−G₁ for the state of the second pair of voltage level shifter switches180;

G₀ for the state of the third pair of voltage level shifter switches190;

G₁ for the state of the fourth pair of voltage level shifter switches198; and

(G₁,G₀) for the state of the demultiplexer 214.

As a specific instance of the above example, suppose the two-bit counterstate is (1, 1). The controller 216 maps this two-bit counter state tothe Gray code (1, 0), where G₁=1 and G₀=0. For the first anti-aliasingfilter switch 140, the controller 216 evaluates the Boolean functionG₁G₀+(−G₁)(−G₀) to set its state. For this specific instance, thecontroller 216 evaluates this Boolean function to 0, indicating that thefirst anti-aliasing filter switch 140 is off (open). The controller 216sets the states of the other switches and the demultiplexer 214 asprovided by the Boolean functions described above.

Some or all of the components illustrated in FIG. 1 can be integrated onone or more die. For example, a dashed rectangle labeled 101 in FIG. 1denotes an example of the components that can be integrated on a singledie.

The common-mode noise filters 162, 202, 208, and 211 filter outcommon-mode noise when measuring the battery cells 102, 104, 106, and108. The common-mode filters can be implemented as passive filters, asdescribed with respect to FIG. 2 below. The bulk current injectionfilters 150, 204, 210, and 212 reduce the effects of common-mode anddifferential-mode currents causing unintentional reception and radiationof electromagnetic radiation. The bulk current injection filters can beimplemented as passive filters, as described with respect to FIG. 2below. The voltage level shifters 112, 164, 184, and 192 level shifttheir respective input voltages to a lower voltage so that circuitcomponents coupled to their respective output are in a lower voltagedomain. The voltage level shifters can be implemented with passive andactive components, as described with respect to FIG. 2 below. Theanti-aliasing filters 118 and 170 filter their respective inputs tomitigate aliasing that might arise due to the analog-to-digitalconverter 110 sampling their respective outputs. The unity gaindifferential buffer 130 buffers the output of the anti-aliasing filters118 and 170.

FIG. 2 shows particular examples of some of the circuit modules shown inFIG. 1. These examples may find use in a variety of applications,including EV applications, and more particularly in tandem with batterycells used in EVs. A battery 502 is coupled to a common-mode noisefilter 504, the common-mode noise filter 504 comprising an inductor 506and a capacitor 508. The common-mode noise filter 504 is an example ofany one of the common-mode noise filters 162, 202, 208, and 211. A pairof switches 510 couples the common-mode noise filter 504 to a bulkcurrent injection filter 512. The bulk current injection filter 512comprises a resistor 514 coupled to a capacitor 516, and a resistor 520coupled to a capacitor 518, where the capacitor 516 is coupled to thecapacitor 518. The bulk current injection filter 512 is an example ofany one of the bulk current injection filters 150, 204, 210, and 212. Avoltage level shifter 522 is coupled to the bulk current injectionfilter 512. The voltage level shifter 522 comprises an operationalamplifier 524 with a first output port and a first input port coupled toresistors 526 and 528, and a second output port and a second input portcoupled to resistors 530 and 532. The voltage level shifter 522 is anexample of any one of the voltage level shifters 112, 164, 184, and 192.An anti-aliasing filter 534 is coupled to the voltage level shifter 522.The anti-aliasing filter 534 comprises a resistor 536 coupled to acapacitor 538, and a resistor 540 coupled to the capacitor 538. Theanti-aliasing filter 534 is an example of any one of the anti-aliasingfilers 118 and 170. As described with respect to the example of FIG. 1,a unity gain differential buffer 542 is coupled to the anti-aliasingfilter 534, and an analog-to-digital converter 544 is coupled to theunity gain differential buffer 542. The unity gain differential buffer542 is an example of the unity gain differential buffer 130.

FIG. 3 depicts a system 300 to monitor the voltage of several batterycells. The system 300 comprises: a first voltage level shifter 302comprising a differential input port, labeled 304 and 306, and adifferential output port, labeled 308 and 310; and a first anti-aliasingfilter 312 comprising a differential input port, labeled 314 and 316,coupled to the differential output port 308 and 310 of the first voltagelevel shifter 302, and a differential output port, labeled 317 and 318;a unity gain differential buffer 320 comprising a differential inputport, labeled 322 and 324, and a differential output port, labeled 326and 328; a first pair of anti-aliasing filter switches 330 to couple thedifferential output port 317 and 318 of the first anti-aliasing filter312 to the differential input port 322 and 324 of the unity gaindifferential buffer 320. The system 300 further comprises: a first bulkcurrent injection filter 332 comprising a differential output port,labeled 334 and 336, and a differential input port, labeled 338 and 340;a first pair of bulk current injection filter switches 342 to couple thedifferential output port 334 and 336 of the first bulk current injectionfilter 332 to the differential input port 304 and 306 of the firstvoltage level shifter 302; and an analog-to-digital converter 344coupled to the differential output port 326 and 328 of the unity gaindifferential buffer 320. In the example of system 300, theanalog-to-digital converter comprises: a sigma-delta modulator 346coupled to the differential output port 326 and 328 of the unity gaindifferential buffer 320; and a cascaded integrator comb filter 348coupled to the sigma-delta modulator 346.

The system 300 further comprises a first battery cell 350 coupled to thedifferential input port 338 and 340 of the first bulk current injectionfilter 332. The system 300 further comprises a first pair of batteryswitches 352 to couple the first battery cell 350 to the differentialinput port 338 and 340 of the first bulk current injection filter 332.In the example of system 300, a first common-mode noise filter 354couples the first battery cell 350 to the first pair of battery switches352.

The system 300 further comprises: a second voltage level shifter 356comprising a differential input port, labeled 358 and 360, and adifferential output port, labeled 362 and 364; a second anti-aliasingfilter 366 comprising a differential input port, labeled 368 and 370,coupled to the differential output port 362 and 364 of the secondvoltage level shifter 356, and a differential output port, labeled 372and 374; and a second pair of anti-aliasing filter switches 376 tocouple the differential output port 372 and 374 of the secondanti-aliasing filter 366 to the differential input port 322 and 324 ofthe unity gain differential buffer 320.

The system 300 further comprises: a second bulk current injection filter378 comprising a differential output port, labeled 380 and 382, and adifferential input port, labeled 384 and 386; and a second pair of bulkcurrent injection filter switches 388 to couple the differential outputport 380 and 382 of the second bulk current injection filter 378 to thedifferential input port 358 and 360 of the second voltage level shifter356. The system 300 further comprises a second battery cell 390 coupledto the differential input port 384 and 386 of the second bulk currentinjection filter 378; a second pair of battery switches 392 to couplethe second battery cell 390 to the differential input port 384 and 386of the second bulk current injection filter 378. In the example ofsystem 300, a second common-mode noise filter 394 couples the secondbattery cell 390 to the second pair of battery switches 392.

The system 300 further comprises: a third bulk current injection filter396 comprising a differential output port, labeled 398 and 400, and adifferential input port, labeled 402 and 404; a third pair of bulkcurrent injection filter switches 406 to couple the differential outputport 398 and 400 of the third bulk current injection filter 396 to thedifferential input port 304 and 306 of the first voltage level shifter302. The system 300 further comprises a third battery cell 408 coupledto the differential input port 402 and 404 of the third bulk currentinjection filter 396; a third pair of battery switches 410 to couple thethird battery cell 408 to the differential input port 402 and 404 of thethird bulk current injection filter 396. In the example of system 300, athird common-mode noise filter 412 couples the third battery cell 408 tothe third pair of battery switches 410.

The system 300 further comprises: a fourth bulk current injection filter414 comprising a differential output port, labeled 416 and 418, and adifferential input port, labeled 420 and 422; and a fourth pair of bulkcurrent injection filter switches 424 to couple the differential outputport 416 and 418 of the fourth bulk current injection filter 414 to thedifferential input port 358 and 360 of the second voltage level shifter356. The system 300 further comprises a fourth battery cell 426 coupledto the differential input port 420 and 422 of the fourth bulk currentinjection filter 414; a fourth pair of battery switches 428 to couplethe fourth battery cell 426 to the differential input port 420 and 422of the fourth bulk current injection filter 414. In the example ofsystem 300, a fourth common-mode noise filter 430 couples the fourthbattery cell 426 to the fourth pair of battery switches 428. The system300 shows four battery cells, but examples can include more than fourbattery cells.

The system 300 further comprises a demultiplexer 432. The demultiplexer432, depending upon its state, provides the output of theanalog-to-digital converter 344 to one of the channels CH1, CH2, CH3, orCH 4. Additional filtering may be performed on the data provided on thechannels CH1, CH2, CH3, or CH 4.

The system 300 further comprises a controller 434. The controller 434 isa finite state machine, where its functionality can be realized byhardware only, by hardware and firmware, by hardware and software, or acombination thereof. When the battery cells are to be monitored, thecontroller 434 closes the pairs of battery switches (352, 392, 410, 428)to connect the battery cells to the various circuit modules. Thecontroller 434 sequences the states of the bulk current injection filterswitches (342, 388, 406, 424), the anti-aliasing filter switches (330,376), and the demultiplexer 432 so that data on each channel correspondsto its corresponding battery cell, where CH1 monitors the first batterycell 350, CH2 monitors the second battery cell 390, and so forth.

The controller 434 controls the states of the bulk current injectionfilter switches (342, 388, 406, 424), and the anti-aliasing filterswitches (330, 376) so that when one of the anti-aliasing filters isbeing read by the analog-to-digital converter 344, the otheranti-aliasing filter is being charged. This reduces latency inmonitoring the battery cells while utilizing only two anti-aliasingfilters to reduce die area.

The controller 434 is configured to: switch on and off the first andsecond pairs of bulk current injection filter switches 342 and 388; andswitch on and off the first and second pairs of anti-aliasing filterswitches 330 and 376. More particularly, the controller is configuredto: switch on and off the first and third pairs of bulk currentinjection filter switches 342 and 406 in complementary fashion; switchon and off the second and fourth pairs of bulk current injection filterswitches 388 and 424 in complementary fashion; and switch on and off thefirst and second pairs of anti-aliasing filter switches 330 and 376 incomplementary fashion.

The above way in which the controller 434 controls the various switchescan be described in more detail by the following example, where thecontroller 434 includes a two-bit counter to sequentially sequencethrough the two-bit counter's four states, and where the controller 434evaluates a set of Boolean functions in response to each of the fourstates in order to set the states of the various switches and thedemultiplexer 432. Based upon the evaluation of the set of Booleanfunctions in response to the two-bit counter, the controller 434sequences the states of the bulk current injection filter switches (342,388, 406, 424,), the anti-aliasing filter switches (330, 376), and thedemultiplexer 432. The sequencing of the states and the set of Booleanfunctions are described as follows.

Let the ordered Boolean pair (S₁,S₀) representing the four states of thetwo-it counter, with S₁ and S₀ given by: (0,0), (0,1), (1,0), and (1,1).The controller 434 generates a gray code based upon the Boolean pair(S₁,S₀), where controller 434 uses the gray code to generate inputs tothe set of Boolean functions. The controller 434 generates the gray codebased on the two-bit counter by the following mapping (S₁,S₀)→(G₁,G₀):(0,0)→(0,0), (0,1)→(0,1), (1,0)→(1,1), and (1,1)→(1,0).

The set of Boolean functions can be described as follows, where “-”denotes a Boolean complement, a product denotes a logical AND, a sumdenotes a logical OR, and where a Boolean function evaluated to aBoolean “1” denotes that its corresponding switch is on and whenevaluated to a Boolean “0” denotes that its corresponding switch is off:

G₁ G₀+(−G₁)(−G₀) for the state of the first anti-aliasing filter switch330;

(−G₁)G₀+(G₁)(−G₀) for the state of the second anti-aliasing filterswitch 376;

−G₀ for the state of the first pair of bulk current injection filterswitches 342;

−G₁ for the state of the second pair of bulk current injection filterswitches 388;

G₀ for the state of the third pair of bulk current injection filterswitches 406;

G₁ for the state of the fourth pair of bulk current injection filterswitches 424; and

(G₁,G₀) for the state of the demultiplexer 432.

As a specific instance of the above example, suppose the two-bit counterstate is (1, 1). The controller 434 maps this two-bit counter state tothe Gray code (1, 0), where G₁=1 and G₀=0. For the first anti-aliasingfilter switch 330, the controller 434 evaluates the Boolean functionG₁G₀+(−G₁)(−G₀) to set its state. For this specific instance, thecontroller 434 evaluates this Boolean function to 0, indicating that thefirst anti-aliasing filter switch 330 is off (open). The controller 434sets the states of the other switches and the demultiplexer 432 asprovided by the Boolean functions described above.

Some or all the components illustrated in FIG. 3 can be integrated onone or more die. For example, a dashed rectangle labeled 301 in FIG. 1denotes an example of the components that can be integrated on a singledie. The common-mode noise filters (354, 394, 412, 430), the bulkcurrent injection filters (332, 378, 396, 414), the voltage levelshifters (302, 356), the anti-aliasing filters (312, 366), the unitygain differential buffer 320, and the analog-to-digital converter 344 ofthe example illustrated in FIG. 3 can have the same structures as theircorresponding counterparts in FIG. 1 as illustrated in FIG. 2.

For every grouping of four battery cells, the example of FIG. 1 utilizesfour voltage level shifters, with each voltage level shifter followed bya pair of voltage level shifter switches. For every grouping of fourbattery cells, the example of FIG. 3 utilizes two voltage level shifterscoupled directly to their respective anti-aliasing filters. However, thepairs of bulk current injection switches in the example of FIG. 3 are ina relatively high voltage domain because they are configured in thesystem 300 at the input side of the voltage level shifters, whereas thepairs of voltage level shifter switches in the example of FIG. 1 areconfigured in the system at the output side of the voltage levelshifters.

Some example circuits may include more than two bulk current injectionfilters coupled to a particular anti-aliasing filter. For example, inthe example of FIG. 1, the bulk current injection filters 150 and 210can each, in turn, be coupled to the anti-aliasing filter 118. However,in some example circuits more than two bulk current injection filtersare configurable to be coupled to an anti-aliasing filter at anyparticular instant of time. Furthermore, some example circuits mayinclude more than two anti-aliasing filters. For example, for an examplecircuit having three anti-aliasing filters, one of the threeanti-aliasing filters may be in the process of being read while theother two anti-aliasing filters are being charged.

Example circuits can be used in a wide variety of applications formonitoring multi-cell battery systems, such as, for example, automotiveapplications. FIG. 4 shows a system 600 in which example circuits canfind application, where the system 600 is part of an automobile orvehicle. The system 600 includes a battery system 602 comprisingmultiple cells. The battery system 602 can be used as the mainelectrical power source in a hybrid or all-electric vehicle. In otherapplications, vehicle electrical systems are expected to be operated atvoltages higher than the traditional 12V systems, so that in suchapplications the battery system 602 can include a relatively largenumber of cells. A battery monitoring system 604 comprises examplecircuits, such as that of FIG. 1 and FIG. 3, to monitor the voltages ofthe cells within the battery system 602. The monitored voltages for eachcell in the battery system 602 are provided to a vehicle electricalmanagement system 606. The vehicle electrical management system 606 canbe part of a vehicle control system for monitoring the status of themany components and system used in automotive vehicles.

In the foregoing discussion and in the claims, the terms “including” and“comprising” are used in an open-ended fashion, and thus should beinterpreted to mean “including, but not limited to . . . .” Also, theterm “couple” or “couples” is intended to mean either an indirect ordirect connection. Thus, if a first device couples to a second device,that connection may be through a direct connection or through anindirect connection via other devices and connections. Similarly, adevice coupled between a first component or location and a secondcomponent or location may be through a direct connection or through anindirect connection via other devices and connections. An element orfeature that is “configured to” perform a task or function may beconfigured (e.g., programmed or structurally designed) at a time ofmanufacturing by a manufacturer to perform the function and/or may beconfigurable (or re-configurable) by a user after manufacturing toperform the function and/or other additional or alternative functions.The configuring may be through firmware and/or software programming ofthe device, through a construction and/or layout of hardware componentsand interconnections of the device, or a combination thereof.Additionally, uses of the phrases “ground” or similar in the foregoingdiscussion are intended to include a chassis ground, an Earth ground, afloating ground, a virtual ground, a digital ground, a common ground,and/or any other form of ground connection applicable to, or suitablefor, the teachings of the present disclosure. Unless otherwise stated,“about,” “approximately,” or “substantially” preceding a valuemeans+/−10 percent of the stated value.

The above discussion is meant to be illustrative of the principles andvarious examples of the present disclosure. Numerous variations andmodifications will become apparent to those skilled in the art once theabove disclosure is fully appreciated. It is intended that the followingclaims be interpreted to embrace all such variations and modifications.

What is claimed is:
 1. A battery-operated device comprising: a firstbattery cell having a voltage; a second battery cell having a voltage; afirst anti-aliasing filter operable to be coupled to the first batterycell; a second anti-aliasing filter operable to be coupled to the secondbattery cell; an analog-to-digital converter operable to be coupled tothe first anti-aliasing filter during a first period of time or thesecond anti-aliasing filter during a second period of time differentthan the first period of time; and wherein the second anti-aliasingfilter is charged during the first period of time and the firstanti-aliasing filter is charged during the second period of time.
 2. Thebattery-operated device of claim 1, wherein the analog-to-digitalconverter outputs a digital representation of the voltage of the firstbattery cell at the first period of time.
 3. The battery-operated deviceof claim 1, wherein the analog-to-digital converter outputs a digitalrepresentation of the voltage of the second battery cell at the secondperiod of time.
 4. The battery-operated device of claim 1, wherein thebattery-operated device is an electric vehicle.